U.S. patent number 6,467,946 [Application Number 09/841,468] was granted by the patent office on 2002-10-22 for method and apparatus for mixing liquid samples in a container using rotating magnetic fields.
This patent grant is currently assigned to Dade MicroScan Inc.. Invention is credited to Peter Louis Gebrian.
United States Patent |
6,467,946 |
Gebrian |
October 22, 2002 |
Method and apparatus for mixing liquid samples in a container using
rotating magnetic fields
Abstract
Mixing a liquid solution in a container by rotating a pair of
bar-shaped magnets in a coordinated pattern in which lines parallel
to the axes of the bar-shaped magnets remain normal to one another,
the magnets disposed in close proximity to and on opposite sides of
the container a distance above the bottom of the container so that
a magnetic mixing member is caused to rotate in the liquid about
the same distance above the bottom of the container. Relative
vertical movement of the magnets and the container generates a
vortex-like mixing action throughout the container.
Inventors: |
Gebrian; Peter Louis
(Wilmington, DE) |
Assignee: |
Dade MicroScan Inc.
(Sacramento, CA)
|
Family
ID: |
25284956 |
Appl.
No.: |
09/841,468 |
Filed: |
April 24, 2001 |
Current U.S.
Class: |
366/273 |
Current CPC
Class: |
B01F
7/005 (20130101); B01F 13/0818 (20130101); B01F
2215/0037 (20130101) |
Current International
Class: |
B01F
13/08 (20060101); B01F 13/00 (20060101); B01F
15/00 (20060101); B01F 013/08 () |
Field of
Search: |
;366/208,209,212,218,219,273,274 ;416/3 ;417/420 ;464/29 ;435/302.1
;266/234 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
3344754 |
|
Jun 1985 |
|
DE |
|
2082929 |
|
Mar 1982 |
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GB |
|
2082930 |
|
Mar 1982 |
|
GB |
|
63-185435 |
|
Aug 1988 |
|
JP |
|
Primary Examiner: Cooley; Charles E.
Attorney, Agent or Firm: Jordan; Leland K.
Claims
What is claimed is:
1. A method for mixing a liquid solution contained in a container
having a false bottom, the method comprising: placing a
ferromagnetic mixing member within the liquid solution contained in
the container; and, rotating a pair of magnetic fields in a
circular pattern in close proximity to the container near the
location of the false bottom, wherein rotating the pair of magnetic
fields comprises rotating a pair of magnets in a coordinated
pattern in which lines parallel to the axes of the magnets remain
normal to one another, so that magnetic forces acting upon the
mixing member cause it to revolve thereby generating a mixing
motion within the liquid solution.
2. The method of claim 1 wherein the pair of magnetic fields are
rotated in close proximity to opposite sides of the container.
3. The method of claim 1 wherein the magnets comprises bar-shaped
permanent or semi-permanent magnets.
4. The method of claim 1 wherein rotating the magnetic fields
comprises rotating a pair of disks containing said magnets in a
coordinated pattern in which the magnetic fields of the two
separate magnets are 90 degrees out of phase with one another.
5. The method of claim 1 wherein the mixing member is
spherical.
6. The method of claim 1 wherein the mixing member is made of an
iron alloy and has a diameter in the range 2-6 mm.
7. The method of claim 1 wherein the mixing member has a protective
coating to prevent contamination having thickness about 25
microns.
8. The method of claim 7 wherein the protective coating comprises a
material selected from the group consisting of parylene, SURLYN.TM.
and TEFLON.TM. plastics.
9. The method of claim 1 wherein the liquid container is supported
within a rack and the rack is moved through the rotating magnetic
fields.
10. A method for mixing a liquid solution contained in a container,
the method comprising: placing a ferromagnetic mixing member within
the liquid solution contained in the container; rotating a pair of
magnetic fields in a circular pattern in close proximity to the
container; and, moving the container vertically relative to the
magnetic fields so that magnetic forces acting upon the mixing
member cause it to revolve thereby generating a mixing motion
throughout the entirety of the liquid solution.
11. The method of claim 10 for mixing a liquid solution contained
in a container wherein rotating the pair of magnetic fields
comprises rotating a pair of bar-shaped magnets in a coordinated
pattern in which lines parallel to the axes of the bar-shaped
magnets remain normal to one another.
12. The method of claim 10 wherein the magnetic fields are rotated
in close proximity to opposite sides of the container.
13. The method of claim 10 wherein the ferromagnetic mixing member
is spherical.
14. An apparatus for mixing a liquid solution within a liquid
container, the apparatus comprising: a liquid container having a
false bottom; a spherical ferromagnetic mixing member within the
liquid in the container; a pair of magnetic field sources
positioned at opposite sides of the container proximate the false
bottom; and, means for rotating the magnetic field sources in
circular patterns in close proximity to the liquid container,
wherein the means for rotating the magnetic field sources comprise
rotating a pair of bar-shaped magnets in a coordinated pattern in
which lines parallel to the axes of the bar-shaped magnets remain
normal to one another, so that magnetic forces acting upon the
magnetic mixing member cause it to rotate, thereby generating a
mixing motion within the liquid solution.
15. The apparatus of claim 14 wherein the magnetic field sources
are rotated in close proximity to the sides of the liquid
container.
16. The apparatus of claim 14 for mixing a liquid sample solution
within a liquid container wherein rotating the magnetic field
sources comprises rotating a motor shaft having said magnetic field
sources attached thereto.
Description
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for
uniformly mixing liquid samples, reagents, or other solutions in a
container. In particular, the present invention provides a method
for rapidly and uniformly mixing a liquid by using a pair of
magnetic field sources rotating near the sides of the container to
generate a vortex mixing action within the liquid.
BACKGROUND OF THE INVENTION
Automated microbiology and clinical chemistry analyzers identify
the presence of microorganisms and analytes in body fluids such as
urine, blood serum, plasma, cerebrospinal fluid, sputum and the
like. Automated microbiology and clinical chemistry analyzers
improve productivity and enable the clinical laboratory to meet the
workload resulting from high-test volume. Automated systems provide
faster and more accurate results as well as valuable information to
clinicians with regard to the types of antibiotics or medicines
that can effectively treat patients diagnosed with infections or
diseases. In a fully automated analyzer, many different processes
are required to identify microorganisms or analytes and an
effective type of antibiotic or medicine. Throughout these
processes, patient liquid samples and samples in combination with
various liquid reagents and antibiotics, are frequently required to
be mixed to a high degree of uniformity producing a demand for high
speed, low cost mixers that occupy a minimal amount of space.
Analyzers like those described above perform a variety of
analytical processes upon microbiological liquid samples and in
most of these, it is critical that a patient's biological sample,
particularly when in a liquid state, be uniformly mixed with
analytical reagents or diluent or other liquids or even re-hydrated
compositions and presented to an analytical module in a uniformly
mixed state. In a biochemical analyzer, other liquids like broth
may need to be uniformly stirred before being used. Various methods
have been implemented to provide a uniform sample solution mixture,
including agitation, mixing, ball milling, etc.
One popular approach involves using a pipette to alternately
aspirate and release a portion of liquid solution within a liquid
container. Magnetic mixing, in which a vortex mixing action is
introduced into a solution of liquid sample and liquid or
non-dissolving reagents, herein called a sample liquid solution,
has also been particularly useful in clinical and laboratory
devices. Typically, such magnetic mixing involves rotating or
revolving a magnetic field beneath the bottom of a container so as
to cause a magnetically susceptible mixing member to rotate in a
generally circular path in a plane inside the container at the
bottom of the container. Thus, such magnetic mixers require that a
magnetically susceptible mixing member be placed in close
proximity, essentially in physical contact, with the bottom of the
container.
Magnetic mixers that cause a magnetically susceptible mixing member
to rotate or revolve at the bottom level or top level of liquid in
a container are not useable in the instance of so-called
"false-bottom" sample containers. False-bottom containers have the
same general size as standard containers, but have an additional
false bottom located at a predetermined distance above the physical
bottom of the container. False-bottom containers are advantageously
employed in several instances, for instance when it is desired to
decrease the physical size of aspiration means which extract
patient sample from a container. In such cases, the vertical travel
required by the aspirator is decreased as the liquid sample level
is found nearer the top of its container. Using false-bottom
containers also makes it possible to handle smaller-than-normal
liquid samples in containers that also have an extended surface for
carrying bar-code indicia. In other instances and for various
reasons, only a small volume of a patient's sample may be available
and false-bottom containers makes it possible to transport a
smaller-than-normal sample volume within an automated analyzer
without having special handling devices adapted to operate on
smaller-than-normal sample containers. Alternately, in the instance
of magnetic vortex mixing, it may be desirable for reasons of
mixing efficiency to have the source of mixing energy, the mixing
member, located anywhere within the volume of a sample to be mixed
as opposed to having the mixing member located at either the top or
bottom of the sample container. Even further, it may be desirable
for reasons of mixing efficiency for the source of rotational
energy to be vertically moveable relative to the sample liquid
during the mixing process as opposed to having the mixing member
located in a stationary plane within the sample container.
U.S. Pat. No. 5,586,823 describes a magnetic stirrer comprising a
bottle having a base and a stirrer bar of relatively low power
magnetization lying on the bottle base. A permanent magnet of
relatively high power is located beneath and close to the bottle
base, and means for continuously rotating the external permanent
magnet about an axis substantially normal to the bottle base. The
rotating magnetic field causes the stirrer bar to continuously
rotate within the liquid in a plane parallel to and above the
bottle base.
U.S. Pat. No. 5,547,280 discloses a two-part housing magnetic
stirrer having a lower drive and an upper part that forms a
mounting surface for a sample container having a mixing magnet. The
separating surface of the upper and lower parts are approximately
horizontal in the working position. The upper part is made of glass
and, when in its working position, is tightly pressed against an
opposing surface of the lower part to provide a magnetic stirrer
that is sealed against aggressive vapors.
U.S. Pat. No. 5,078,969 discloses a stirrer which is placed on a
reaction vessel and used for staining biological specimens on
microscope slides in a jar. The bottom wall of the jar is
perforated and made of glass so that the magnetic flux passes
through to couple a stirrer rod to a magnetic drive arm. The jar is
seated on a platform with the magnetic-stirrer drive mounted and
operable below the platform. The magnetic drive has a motor with
magnetic drive arm like a permanent magnetic and a variable speed
control device to control the angular velocity of the magnetic
arm.
U.S. Pat. No. 4,728,500 discloses a stirrer comprising a
magnetically permeable vessel containing at least one magnetic bead
and a magnetic device having a spacer with a number of
longitudinally positioned magnetic bars parallel to one another
disposed thereon. The bars may be moved in a longitudinal direction
beneath the vessel so as to produce an oscillating magnetic field
causing the beads to undergo an elliptic motion.
U.S. Pat. No. 4,534,656 discloses a magnetic stirrer apparatus in
which the stirrer is buoyant, and thereby floats on the surface of
a liquid which is to be stirred. The stirrer is caused to be
rotated, generally about the vertical axis of the flask, and is
enabled to change its elevation, relative to the bottom of the
flask, as the level of liquid in the flask is changed. The floating
stirrer is restricted by a guide rod to rotational movement, and to
vertical movement as the liquid level changes; a magnetic drive is
provided to cause rotational movement of the stirrer, thereby to
mix the liquid in the flask.
U.S. Pat. No. 4,162,855 discloses a magnetic rotor having a central
hub which has a surface covered with an inherently high lubricity
material and on which is mounted a radially extending magnetic
impeller. The magnetic rotor is mounted in a central collar portion
of a cage which has a number of frame members extending from the
collar to prevent the rotating impeller from engaging the walls of
the vessel. As the outward members maintain the cage in position
within the vessel, the magnetic rotor is allowed to "float"
relative to the cage and rotate freely, with extremely low
frictional forces, relative to the vessel to agitate the substance
therein.
Accordingly, from a study of the different magnetic mixers
available in the prior art, there is an unmet need for an improved
magnetic vortex mixer capable of magnetically mixing small volume
liquid samples held within false-bottom containers. In addition,
there is a need for a magnetic mixer which provides a uniform
mixing action within liquid samples contained in false-bottom tubes
held in a sample tube rack without removing the sample tubes from
the rack so as to eliminate the need for time-consuming and
spacious mechanisms to move the tube to a separate location for
mixing. There is a further need for magnetic mixing method having
increased efficiency by moving the mixing member along an axis of
the sample container during the mixing process, as may be required
for low viscosity liquid samples.
SUMMARY OF THE INVENTION
Many of these disadvantages to the prior art are overcome by using
the apparatus and/or methods of this invention. This invention
provides a method for mixing a liquid solution contained in a
container by causing a freely disposed, magnetically susceptible
mixing member to rotate or revolve in a generally circular pattern
in a plane above the physical bottom of the container. The magnetic
mixing member may have a spherical or oblong shape and is caused to
rotate within the solution by revolving a pair of magnetic field
sources external to the liquid container in a plane above the
physical bottom of the container in a generally circular pattern.
Rotation of the magnetic field sources is controlled so that the
combined magnetic fields acting upon the magnetic mixing member
cause it to rotate and generate a mixing motion within the liquid
solution. In an exemplary embodiment, the magnetic field sources
are diametrically opposed along the sides of and are in close
proximity to a false bottom of a liquid sample container and are
rotated in a coordinated motion. In an alternate embodiment, the
magnetic field sources are rotated at diametrically opposed
positions along a liquid sample container and the liquid sample
container is moved upwards or downwards relative to the magnetic
field sources.
In any of these embodiments, multiple liquid solutions held in
liquid containers supported in a rack may be simultaneously mixed
by moving the rack through the revolving magnetic fields while the
containers remain within the rack. In an exemplary embodiment, the
small magnetic mixing member is shaped like a spherical ball and
may be automatically dispensed either at time of manufacture of the
liquid sample container or loaded on-board the instrument into a
liquid solution container easily. Such a spherical mixing member
may be produced in large quantities at very low cost so that it may
be discarded after a single use in contrast to prior art stirring
members that are typically expensive plastic-coated permanent
magnets and are therefore repeatedly used, increasing risk of
contamination.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood from the following
detailed description thereof taken in connection with the
accompanying drawings which form a part of this application and in
which:
FIG. 1 is a schematic elevation view of a magnetic mixing apparatus
that may be used to advantage in practicing the present invention
with false bottom sample containers;
FIG. 2 is a top plan view of a mixing disk useful in practicing the
invention of FIG. 1;
FIGS. 3A-3K are schematic illustrations of coordinated motion of a
pair of magnetic field sources revolving in a plane above the
physical bottom of a container as taught by the present
invention;
FIG. 4 is a schematic elevation view of a alternate exemplary
magnetic mixing apparatus in which magnetic field sources are
rotated at opposite locations of a liquid sample container having a
false bottom and the container is moveable between the rotating
magnetic field sources as taught by the present invention;
FIG. 5 is a schematic elevation view of another exemplary magnetic
mixing apparatus in which magnetic field sources are rotated at
opposite locations of a conventional liquid sample container and
the container is moveable between the rotating magnetic field
sources as taught by the present invention;
FIGS. 6A and 6B are schematic front and side elevation views of a
magnetic mixing apparatus that may be used to mix a number of
liquid solutions held in liquid sample containers without removing
the containers from a support rack when practicing the present
invention; and,
FIG. 7 is a cross-section view of a mixing member that may be
employed to advantage in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the elements of a magnetic mixing apparatus 10
comprising a pair of magnetic field sources 12 disposed at
diametrically opposite locations alongside a liquid container 14
and having sufficient magnetic strength so that the combined
non-uniform magnetic forces acting on a mixing member 16 produced
by revolving the magnetic field sources 12 generate an effective
mixing motion within a liquid sample 18 within the liquid container
14. In a highly effective embodiment of the present invention, the
magnetic field sources 12 are bar-shaped magnets 12 having opposed
north-pole and south-pole ends and are diametrically opposed at
positions along the side of container 14 that correspond to the
location of a false bottom 20 within container 14. Liquid container
14 comprises a lower empty portion 13 containing air and separated
and sealed from an upper portion 15 containing liquid sample 18.
For convenience, a pair of motors 22 provide rotation to motor
shafts 24 having disks 26, each encasing a bar-shaped magnet 12
with its cylindrical axes intersecting north-pole end N and an
opposed south-pole end S.
FIG. 2 is a top plan view of such a disk 26 encasing the bar-shaped
magnets 12 showing the axis A of such a bar-shaped magnet 12.
Rotation of disks 26 by motor shafts 24 in a coordinated pattern
described hereinafter produces a combined rotating magnetic field
acting on mixing member 16 which causes mixing member 16 to rotate
in a generally circular pattern within liquid 18 thereby generating
a vortex-like mixing motion of liquid 18. Additionally, the present
invention may be practiced by reversing or alternating the
direction of rotational motion of the magnetic field sources 12
during mixing to induce a shear-agitation mixing motion of liquid
18.
Mixing member 16 may be formed, for example, like a bar or ball 16
of ferromagnetic or semi-ferromagnetic material (see FIG. 7).
Hereinafter the term ferromagnetic is intended to mean a substance
having a sufficiently high magnetic permeability to be positionally
affected by an orbiting or rotating magnetic field. Mixing member
16 is sized and has a sufficiently high magnetic permeability so
that the magnetic field forces generated by magnetic field sources
12 are greater than forces of gravity acting upon mixing member 16.
The term magnetic is likewise intended to mean a substance that is
independently capable of generating a magnetic field. Liquid
container 14 is of a non-magnetic material and may be supported in
an upper section of a mixing stand (not shown for clarity
purposes), the mixing stand also having with lower section designed
to encase motors 22.
It has been discovered that a highly effective mixing or agitation
action occurs in liquid sample 18 using the above described
combination of revolving bar-shaped mixing magnets 12 and mixing
member 16 when the bar-shaped magnets 12 are revolved in a same
first direction at diametrically opposed locations across liquid
container 14 in a pattern that causes mixing member 16 to revolve
in a second direction opposite to the first direction. It has been
found that the most effective embodiments of the present invention
comprise controlling the relative rotation of bar-shaped magnets 12
so that the separate magnetic fields of the two separate bar-shaped
magnets 12 are 90 degrees out of phase with one another.
Consequently, the separate magnetic fields interact to produce a
single magnetic field that rotates in a direction opposite to the
direction of rotation of the bar-shaped magnets 12.
FIGS. 3A-K are schematic top plan views of mixer 10 and illustrate
an embodiment of the present invention wherein two bar-shaped
mixing magnets 12 encased in disks 26 are rotated by motor shafts
24 in a clockwise direction so that cylindrical axes of the
bar-shaped magnets remain normal to one another. Thus, the magnetic
fields of the two separate bar-shaped magnets 12 are 90 degrees out
of phase with one another, as described above. Such a synchronized
rotation produces a single magnetic field that rotates in a
direction opposite to the direction of rotation of the bar-shaped
magnets 12, thereby causing mixing member 16 to rotate in a
counter-clockwise direction within liquid sample 18 contained
within liquid container 14. As shown in FIG. 1, disks 26 are
located at a vertical location along the side of container 14 that
corresponds to the location of false bottom 20 within container 14
so that an effective vortex-like mixing action takes place in
liquid sample 18 even though lower portion 13 contains air and is
separated from upper portion 15 containing liquid sample 18. FIGS.
3A-K are a "slow-motion" description of the mixing process of the
present invention.
FIG. 3A shows two disks 26L and 26R comprising bar-shaped mixing
magnets 12L and 12R and being diametrically disposed on opposite
left-hand and right-hand sides, respectively, of a liquid container
14 containing sample 18 to be mixed. Disks 26L and 26R are
essentially identical but are assigned different numbers in FIG.
3A-K for purposes of describing the present invention. In FIG. 3A,
disk 26R is shown in a initial stationary position so that, for
example, mixing member 16 is aligned with the south-pole end S of
mixing magnet 12R along the cylindrical axis AR of magnet 12R. In
this initial mixing positioning, disk 26L is oriented so that
cylindrical axis AL of mixing magnet 12L is normal to cylindrical
axis AR. Obviously the relative positions of north-pole end N and
the south-pole end S could be reversed in both magnets 12L and 12R
and yield an identical mixing process. This 90-degree phase
difference between mixing magnet 12R and mixing magnet 12L is
maintained throughout the mixing process of the present invention
in order to produce a net magnetic field that rotates in a
direction opposite to the direction of rotation of the bar-shaped
magnets 12R and 12L.
FIG. 3B illustrates a first mixing stage subsequent to the initial
position of FIG. 3A whereat both disks 26L and 26R have been
rotated clockwise about 45 degrees. At this position, a net
magnetic field different from that of FIG. 3A results from the
changed positions of mixing magnets 12L and 12R. In this first
mixing stage, mixing member 16 is caused to revolve also about 45
degrees counter-clockwise as a result of the changed positions of
mixing magnets 12L and 12R. Because of the closest proximity to
magnet 12R in the initial position of FIG. 3A, mixing member 16
"chases" the south pole end S of magnet 12R as it provides the
strongest nearby magnetic field. Throughout the mixing process,
mixing member 16 moves throughout the liquid to be mixed as the
mixing member 16 is caused to move in a pattern that minimizes its
physical distance to the nearest magnetic field. As described
previously, it has been discovered that a highly effective mixing
action may be generated within solution 18 by rotating mixing
magnets 12L and 12R so that dashed-line AL drawn through the
cylindrical axis of mixing magnet 12L remains normal to the
dashed-line line AR drawn through the cylindrical axis of mixing
magnet 12R.
FIG. 3C illustrates a second mixing stage subsequent to the first
mixing stage of FIG. 3B whereat both disks 26L and 26R have been
rotated clockwise a total of about 55 degrees. At this position, a
net magnetic field different from that of FIG. 3B results from the
changed positions of mixing magnets 12L and 12R. In this second
mixing stage, mixing member 16 is roughly equidistant from magnetic
pole N of magnet 12L and magnetic pole S of magnet 12R and as disks
26 encasing the bar-shaped mixing magnets 12 are rotated an
additional amount in a clockwise direction, mixing magnet 12L
exerts a greater attraction on mixing member 16 than does mixing
magnet 12R so that mixing member 16 travels towards magnet 12L in a
path that tends to be more linear than circular. This situation
occurs twice during each 360 revolution of the mixing member 16
along its generally circular mixing path.
FIGS. 3D-F illustrate a series of mixing stages subsequent to the
second mixing stage of FIG. 3C whereat both disks 26L and 26R have
been rotated clockwise a total of about 180 degrees from starting
position depicted in FIG. 3A. In each of these stages, a net
magnetic field different from that of a prior stage results from
the changed positions of mixing magnets 12L and 12R. During these
stages, mixing member 16 is caused to revolve about 360 degrees
counter-clockwise as a result of the 180 degree clockwise rotation
of mixing magnets 12L and 12R. Throughout the mixing process, disks
26 encasing the bar-shaped mixing magnets 12 continue to rotate in
a pattern controlled so that cylindrical axis AL of mixing magnet
12L remains normal to the cylindrical axis AR of mixing magnet 12R.
At the mixing stage illustrated by FIG. 3F, disk 26L, disk 26R and
magnetic mixing member 16 are in a magnetically equivalent position
and orientation as that of FIG. 3A. Continuous operation of motors
22 causes motor shafts 24 to continuously rotate in a clockwise
direction so that disks 26L and 26R also continuously rotate
clockwise, as shown in FIGS. G-H-I-J-K, thereby repeating the
counterclockwise rotation of mixing member 16 depicted by FIGS.
3A-F. Because of the viscous shear action generated within liquid
18 by the rotational movement of mixing member 16, a vortex-like
mixing action is created within liquid 18. The present invention is
thus seen to cause freely disposed, magnetically susceptible mixing
member 16 to oscillate in a generally circular pattern anywhere
within the volume of a sample to be mixed as opposed to having the
mixing member located at either the top or bottom of the sample
container.
FIG. 4 shows the elements of an alternate embodiment of magnetic
mixing apparatus 10 in which container 14 is moved vertically
between the revolving mixing magnets 12 so that the rotating
magnetic field acting on mixing member 16 causes mixing member 16
to rotate at a number of different heights or planes within liquid
18.
Equivalently, this alternate embodiment may be practiced by holding
the container 14 stationary and moving motors 22 provided to rotate
mixing magnets 12 as described before vertically along the sides of
container 14. Motion of container 14 "upward and/or downward"
between disks 26L and 26R comprising mixing magnets 12L and 12R is
indicated by bi-directional arrow 27 in FIG. 4. This alternate
embodiment of the present invention is seen to provide a means for
generating a vortex-like mixing action throughout the entirety of
the volume of liquid 18 in distinction to constraining the rotation
of mixing member 16 to be proximate false bottom 20 of container
14.
In an embodiment similar to FIG. 4, as depicted in FIG. 5, a
conventional container 30 not having a false bottom but being
filled with liquid 18 to be mixed may moved vertically between the
revolving mixing magnets 12 so that the rotating magnetic field
acting on mixing member 16 causes mixing member 16 to rotate at a
number of different heights or planes within liquid 18, thereby
mixing liquid 18 throughout its entirety. Such an embodiment may be
particularly useful in the event that liquid 18 is of such low
viscosity that a vortex-like mixing action generated by mixing
member 16 only proximate the bottom 32 of container 30 would be
ineffective or time-wise inefficient in generating a mixing action
throughout the entirety of liquid 18. The embodiment illustrated in
FIG. 5 is also useful in instances wherein it is undesirable to
place a conventional magnetic stirring apparatus beneath a
conventional container as is usual practice in laboratory mixing
devices. Such a situation may arise, for example, whenever it is
important to minimize physical sizes of devices in automated
laboratory analyzers.
In all embodiments, mixing member 16 is preferably formed from a
ferromagnetic or semi-ferromagnetic material and simple rotation of
mixing magnets 12 by motors 22 produces corresponding revolving
magnetic field forces upon mixing member 16 in container 14.
Magnets 12 may comprise, for example, permanent magnets formed of
neodymium-iron-boron (NdFeB) or other similar materials. Successful
mixing of a low viscosity, liquid solution has been accomplished in
about 1/2 second using a 5000 rpm motor 22, from Maxon Motor Co.,
Fall River, Mass., with 1/4 inch diameter.times.3/4 inch long
mixing magnets 12 having field strength 4000 gauss located
diametrically across from and at a distance of about 1/16 inch from
the exterior of container 14. In another exemplary embodiment of
magnetic mixing apparatus 10, a number of liquid containers 14 may
be placed in a multiple-tube mixer block 44, as seen in FIG. 6A and
6B adapted to accommodate a number of tube-like liquid solution
containers 14 in a linear array. Block 44 is transported in the
direction shown by arrow 36 proximate the revolving magnetic field
sources 12 so that the false bottoms 20 of the containers 14 each
having mixing members 16 therein are positioned nearby to the
revolving mixing magnets 12. In this instance, the mixer block 44
may be transported between the revolving mixing magnets 12 and the
liquid solutions 18 within liquid containers 14 are mixed as the
individual liquid containers 14 are positioned proximate thereto.
In such an embodiment, the necessity for removing individual liquid
containers 14 from block 44, as is the conventional practice within
analytical laboratories, to a separate location is eliminated,
thereby saving operating space and the expense of additional
automated mechanisms. In comparison with FIG. 5 conventional tubes
30 may be substituted for false-bottom tubes 14 and disks 26 are
positioned proximate the bottom 32 of tubes 30 so that magnetic
mixing apparatus 10 of the present invention may also be useful in
mixing liquids contained within numbers of conventional tubes.
FIG. 7 is an exemplary illustration of a ball-like mixing member 16
comprising an inner core 40 of ferromagnetic or semi-ferromagnetic
material like an iron alloy and may be optionally coated with a
thin layer 42 of protective, waterproof material like plastic,
paint, epoxy, and the like. Such a ball-like mixing member 16 is
very low in cost, typically less than 1 cent, and may be obtained
from sources like the Epworth Mill, South Hoover, Mich., as a
SAE-52100 Chrome Alloy Spherical Grinding Ball. Various plastic
layers 42 like SURLYN.TM. or TEFLON.TM. plastics, polyethylene, or
parylene plastics may be coated over the surface of mixing member
16 at a thickness of about 25 microns for the purpose of avoiding
contamination (rust, iron oxide, etc.) and thereby maintaining the
integrity of a liquid solution. Such coating services are available
from, for example, PCS, Katy, Tex. In use, a number of these mixing
members 16 may be supplied in a straw-like magazine and
automatically dispensed into the liquid container 14 using any one
of a number of conventional dispensers. Alternately, the mixing
members 16 may be pre-disposed within the liquid container 14
before presentation to the magnetic mixing apparatus 10 and a
number of liquid containers 14 may be supported in a conventional
tube rack so that the liquid solution in the liquid container 14
may be uniformly mixed without removing the liquid containers 14
from the rack.
In an operative example of the present method for mixing a liquid
solution using magnetic mixing apparatus 10 by placing a small,
spherically shaped magnetic mixing member 16 within the liquid
solution and revolving a magnetic field at high speed in a circular
pattern at close proximity to the liquid container 14, a liquid
solution 18 of water and red food dye was placed in a
false-bottomed tube 14 having a diameter about 0.6 inches. A
magnetic mixing member 16 formed of 52100 chrome alloy having a
diameter within the range 2-6 mm was added to the solution within
liquid container 14 like that shown in FIG. 1. Two bar-shaped
mixing magnets 12 of size about 1/4-inch by 3/4-inch were attached
to a pair of motor shafts and the motor supported so that the
mixing magnets 12 were about 1/16-inch from the side of the liquid
container 14. The motor was rotated for about 1/2-second at 5000
rpm and the distribution of dye within the solution was observed to
be thoroughly and uniformly distributed.
It is to be understood that the embodiments of the invention
disclosed herein are illustrative of the principles of the
invention and that other modifications may be employed which are
still within the scope of the invention. For example, obvious
variants of the invention include using 2 separate small magnets to
emulate the bar magnet, or replacing the permanent magnetic field
with an circular electromagnetic field source and varying the
time-intensity pattern of power supplied thereto, employing a
non-spherical mixing member, eliminating the mixer block and
placing the revolving magnetic field proximate to a tube in a rack,
etc. Accordingly, the present invention is not limited to those
embodiments precisely shown and described in the specification but
only by the following claims.
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